Computed tomography (CT) systems and methods are widely used, particularly for medical imaging and diagnosis. CT systems generally create images of one or more sectional slices through a subject's body. A radiation source, such as an X-ray tube, irradiates the body from one side. A collimator, generally adjacent to the X-ray source, limits the angular extent of the X-ray beam, so that radiation impinging on the body is substantially confined to a planar region defining a cross-sectional slice of the body. At least one detector (and generally many more than one detector) on the opposite side of the body receives radiation transmitted through the body substantially in the plane of the slice. The attenuation of the radiation that has passed through the body is measured by processing electrical signals received from the detector.
These conventional detectors are called energy-integrating detectors for acquiring energy integration X-ray data. Recently, photon-counting detectors are configured to acquire the spectral nature of the X-ray source rather than the energy integration nature in acquiring data. To obtain the spectral nature of the transmitted X-ray data, the photon-counting detectors split the X-ray beam into its component energies or spectrum bins and count a number of photons in each of the bins. The use of the spectral nature of the X-ray source in CT is often referred to as spectral CT. Since spectral CT involves the detection of transmitted X-rays at two or more energy levels, spectral CT generally includes dual-energy CT by definition.
The photon-counting detectors may include semiconductor-based CZT or CdTe sensors that have fast electronic readout capability. Semiconductor-based photon-counting detectors used in spectral CT can detect incident photons and measure photon energy for every event. However, at high flux, the CZT or CdTe sensors polarize and thereby stop functioning accurately. The information captured by the polarized sensors is severely distorted and thus is unusable. Utilizing such unusable data during image pre-reconstruction and reconstruction processing phases results in artifacts in the reconstructed CT image. Accordingly, it is essential to identify polarized detector data and process it in an appropriate manner.